Compression resistant rayon staple



United States Patent 3,057,037 COMPRESSKON RESISTANT RAYON STAPLE Rufus T. Carney, Broomall, Pa., and James E. Corr,

Front Royal, Va., assignors to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware No Drawing. Continuation of original application Ser.

No. 729,084, Apr. 17, 1958. This application Dec. 19,

1960, Ser. No. 76,503

2 Claims. (Cl. 28-78) This invention relates to crimpcd fibers of regenerated cellulose and their production. It relates more particularly to crimped regenerated cellulose staple fibers having a high resistance to loss of volume when subjected to compression. It relates further to masses of staple fibers having superior absorbency.

This application is a continuation of patent application Serial No. 729,084, filed April 17, 1958, and now abandoned.

Staple cotton has long been utilized for both medical and non-medical applications in sterile and non-sterile form because of its resistance to compressive deformation, i.e., resistance to loss of interfiber volume (volume between fibers in a mass) when subjected to compression, as well as absorbency and other desirable properties.

Because crimped regenerated cellulose staple fibers are prepared synthetically, they are more uniform, i.e., in physical dimensions, in strength, in freedom from foreign matter and other impurities, etc. It was thus apparent to the users of such fibers that it would be advantageous to be able to substitute crimpcd rayon fibers for cotton. When crimpcd regenerated cellulose staple fibers were first evaluated as a substitute for cotton, however, it was found that they lost a consider-able portion of their bulk when subjected to compression. Moreover, balls of crimpcd regenerated cellulose staple fibers would not only tend to collapse when wet with water thus reducing their interfiber volume, their capacity to absorb fluids was also reduced thereby. Moreover, their feel to the hand was unsatisfactory as compared to cotton. On the other hand, when these balls of rayon staple were used as plugs for test tubes or similar vessels, they sometimes fell out of, or slid into, the vessel during or after sterilization. Since it is known that the regenerated cellulose molecule does not possess cross-linkings in the degree that natural cellulose does, these failings were not entirely unexpected.

It is accordingly an object of this invention to provide crimped regenerated cellulose staple fibers having improved resistance to reduction in interfiber volume when subjected to compression in either the wet or dry state. It is a further object of this invention to provide crimpcd regenerated cellulose staple fibers having improved resistance to reduction in interfiber volume when subjected to the conditions of temperature and humidity encountered in heat sterilization procedures. It is a still further object of this invention to provide crimped regenerated cellulose staple fibers having improved absorbency. A further object is the provision of a unique method for preparing the unique staple fibers of this invention. These and other objects are described below.

In accordance with the present invention, there has been discovered a crimped regenerated cellulose staple fiber which overcomes the failings of the prior art to provide a crimpcd rayon staple fiber which can be used to replace cotton for its uses in the form of balls, rolls, batting, etc. One of the most outstanding properties of the staple fiber of the present invention is i s resistance to reduction in interfiber volume (i.e., resilience). The crimped regenerated cellulose staple fibers of this invention possess a resilience. dry or wet (i.e., resistance to reduction in interfiber volume), not only superior to that of known crimpcd rayon but which is generally superior to that of cotton.

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As indicated above, interfiber volume is defined as the volume between the fibers, in other Words, the difference between the total volume occupied by a mass of fibers and the actual volume occupied by the fibers. The total volume occupied by a mass of fibers includes the volume occupied by the fibers plus the volume occupied by the air between the fibers. The interfiber volume, in essence therefore, measures the, volume of air between the fibers in a given mass thereof and is thus an accurate measure of the resilience of such a mass. Measurement of interfiber volume in both the wet and dry state is utilized herein to illustrate the resistance of the unique fiber of this invention to a loss of volume in accordance with the method described by Gottlieb et al. at page 43, volume XXVIII, No. 1, January 1958 of the Textile Research Journal.

The staple fibers of this invention have a minimum interfiber volume at 0.5 p.s.i., according to the Gottlieb et al., test, of 1.75 cubic inches when dry and 1.00 cubic inches when wet; whereas values approaching 2.70 in the dry state and 1.15 in the wet state have been produced. Moreover, the staple fibers of this invention possess a crimp of at least 19 times the square root of the reciprocal of 'the denier thereof. In a preferred embodiment, the crimp is generally about 19 to 35 times the square root of the reciprocal of the denier at a denier of about 1 to 5.5. Practical working conditions dictate a crimp of 24 to 32 times the square root of the reciprocal of denier, with an average of about 26 to 28 times the square root of the reciprocal of the denier being a satisfactory working limitation. The crim-ped regenerated cellulose staple fibers of this invention also possess a capacity to absorb between about 26 to 35 times their weight of water, with a capacity of 26 to 28 being a satisfactory minimum. Thus this unique staple is as good and frequently a better absorbent than cotton and is greatly superior to crimpcd rayon staple known heretofore. The foregoing absorbency values are obtained according to the method outlined in volume XV, U.S. Pharmacopeia, pages 925-926.

In the unique method of the present invention, there are several novel factors which contribute to the superior properties possessed by the improved crimpcd regenerated cellulose staple fibers of this invention. First of all, in preparing the alkali cellulose, it is essential that an alpha cellulose be used having an ether-extractable solids content (generally wood resins) no higher than 0.05% by weight. Pulps having as low as 0.01% by weight etherextractable solids have been utilized, pulps having a lower resin content being preferred where feasible. It is essential also that the steep soda contain no more than 0.8% by weight hemicellulose, preferably 0.7% or lower. cording to this invention, it is essential also that the caustic soda utilized in the mixing step to dissolve the cellulose xanthate contain substantially no hemicellulose, wood resins or other low molecular weight material derived from the cellulosic source. This contrasts with the usual procedure followed in preparing crimped rayon staple of utilizing caustic soda recovered from the steeping step which contains about 1 to 2% by weight or more hemicellulose. It is also essential to maintain the acid content of the spinning bath between about 5 and 8% by weight H Optimum characteristics are imparted to the staple fiber in the most expeditious manner at concentrations between about 6.5 and 7.0% sulfuric acid. Moreover a stretch of 60 to (preferably 70 to 80%) is essential in accordance with this invention.

Preferable, but not absolutely essential to this invention is the application of a finish to the staple fiber of this invention. For example 0.01 to 0.3% by weight of one of the materials disclosed in U.S. 2,821,489 may be used, preferably 0.1 to 0.2% by weight of the polyoxyethylene glycol monoether of sorbitan monolaurate containing about 15 to 25 (preferably 20) ethylene oxide units/mol;

3 or like quantities of the polyoxyethylene glycol monoether of sorbitan monopalmitate containing to 20 (preferably 16) ethylene oxide units/mol. The finish material may be applied at one of several stages of the preparation, but it is most advantageously applied after the staple is cut, washed and bleached.

In the preferred embodiment of the present invention, generally between about 28 and 35% CS; (based upon weight of alpha cellulose) is utilized in xanthating the cellulose producing thereby, in conjunction with known procedures and the novel ones described above, a viscose containing about 5.5 to 7% by weight of caustic soda, preferably 6.0 to 6.5%, about 7.0 to 95% by weight, preferably 8.0 to 9.0%, of cellulose with a salt test of 5 to 7.5, preferably 5.5 to 6.5. In the preferred embodiment herein, the spinning bath generally contains, in addition to the acid as described above, about to 22% by weight of Na SO or K 50 and about 0.75 to 1.5% ZnSO After stretching, the filaments are then preferably cut to staple length, about 1 to 2 inches, preferably about 1% inches followed by washing and bleaching. For convenient handling, the filaments may be cut directly into a washing bath. In any event, only fresh water washes are utilized in order to assure superior resilience, absorbency, and color; in other words none of the washes are recirculated. After washing the staple fibers are generally bleached in a water solution containing available chlorine in the form of a soluble hypochlorite such as sodium or calcium hypochlorite at a pH of about 9 to 12, preferably 11.5 to 12. In this bleaching treatment the bleach solution should contain sufficient soluble hypochlorite to provide 0.1 to 0.3% by weight available chlorine, preferably about 0.175% available chlorine. Thereafter, the staple fiber is generally finished as described above. In addition to the materials described above, in the preferred procedure, the staple fiber is made discoloration resistant by the use of a bisulfite according to the procedure disclosed and claimed in US. 2,821,489.

The following example illustrates a preferred embodiment of the present invention. It is not, however, a limitation thereon, the scope of the invention being set forth in the appended claims.

Example A quantity consisting of 530 pounds of cellulose pulp containing between 0.01 and 0.05% by weight of etherextractable solids (principally wood resin) was steeped in aqueous caustic soda of about 18.3% by Weight concentration. As the hemicellulose content of the steep solution approached about 0.8% by weight during steeping, a portion of the steeping solution was replaced with fresh caustic soda (18.3%) in order to maintain the hemicellu lose content thereof at 0.7% or lower. After pressing, the alkali cellulose Was shredded in a Pfleiderer and then mercerized for about 44 hours at about 30 C. It was then xanthated with a solution containing about 32.43% by weight of carbon disulfide. The cellulose xanthate was next dissolved in a mixer containing about 220 liters of 18% by weight caustic soda and about 1426 liters of water producing a viscose containing about 6.2% caustic soda and about 8.8% cellulose with a ball fall of about 54 seconds and a salt test of about 6.2. After ripening and deaerating, the viscose is spun into a regenerating bath containing about 6.75% by weight sulfuric acid, 1.0% by Weight zinc sulfate and 20% by weight disodium sulfate at about 50 C. and with a 14 inch immersion. The filaments formed thereby were stretched about 70.8% in the spinning bath to a denier of about 3.0 and then cut to a length of about 1% inches. After washing in water, the fibers were bleached in a sodium hypochlorite solution containing about 0.175 by weight available chlorine and about 0.125% by Weight of caustic soda at a pH of 11.5 to 12. Following neutralization and washing, the fibers were finished with a solution containing about 0.18% by weight of the polyoxyethylene glycol monoether of sorbitan monolaurate containing about 20 ethylene oxide units per mole and about 0.4% by weight of sodium bisulfite at a pH of about 5.0.

We claim:

1. A fibrous product of the type prepared from a viscose formed by reacting cellulose pulp containing not more than about 0.05 by weight of ether-extractable solids with caustic soda containing not more than 0.8% by weight of hemicellulose to form cellulose xanthate and dissolving said xanthate in caustic soda free of hemicellulose to form viscose, said product comprising regenerated cellulose staple fibers having a denier of from about 1 to 5.5 and crimps comprising helical bends numbering per inch 19 to 35 times the square root of the reciprocal of said denier, said staple fibers having the property of retaining said crimps when wet and in a relaxed state, a quantity of about 1.5 grams of said staple fibers having an interfiber volume in the dry state of at least 1.750 cubic inches when subjected to a pressure of 0.5 pound per square inch and an interfiber volume in the wet state of at least 1.000 cubic inches when subjected to a pressure of 0.5 pound per square inch, and having the capacity to absorb 26 to 35 times its weight of Water.

2. A fibrous product of the type prepared from a viscose formed by reacting cellulose pulp containing 0.01 to 0.05 by weight of ether-extractable solids with caustic soda containing not more than 0.7% by weight of hemicellulose to form cellulose xanthate and dissolving said Xanthate in caustic soda free of hemicellulose, said product comprising regenerated cellulose staple fibers having a denier of from about 1 to 5.5 and crimps comprising helical bends numbering per inch 26 to 28 times the square root of the reciprocal of said denier, said staple fibers having the property of retaining said crimps when wet and in a relaxed state, a quantity of about 1.5 grams of said staple fibers having an interfiber volume in the dry state of at least 1.750 cubic inches when subjected to a pressure of 0.5 pound per square inch and an interfiber volume in the wet state of at least 1.000 cubic inches when subjected to a pressure of 0.5 pound per square inch and having the capacity to absorb 26 to 28 times its weight of water.

References Cited in the file of this patent UNITED STATES PATENTS 2,222,050 Stoeckly Nov. 19, 1940 2,369,191 Thurmond Feb. 13, 1945 2,383,900 Briarclitf Aug. 28, 1945 2,451,558 Schlosser Oct. 19, 1948 2,686,709 Woodell Aug. 17, 1954 2,821,489 McNeer Jan. 28, 1958 2,834,093 Woodell May 13, 1958 2,968,858 Brenner et a1 Jan. 24, 1961 2,986,446 Smith et a1 May 30, 1961 OTHER REFERENCES Hermans, P. H.: Physics and Chemistry of Cellulose Fibres, Elsevier Publishing C0., N.Y. (1949), pp. 324 and 333 of interest. 

1. A FIBROUS PRODUCT OF THE TYPE PREPARED FROM A VISCOSE FORMED BY REACTING CELLULOSE PULP CONTAINING NOT MORE THAN ABOUT 0.05% BY WEIGHT OF ETHER-EXTRACTABLE SLOLIDS WITH CAUSTIC SOD CONTAINING NOT MORE THAN 0.8% BY WEIGHT OF HEMICELLULOSE TO FORM CELLULOSE XANTHATE AND DISSOLVING SAID ZANTHATE IN CAUSTIC SODA FREE OF HEMICELLULOSE TO FORM VISCOSE, SAID PRODUCT COMPRISING REGENERATED CELLUSLOSE STAPLE FIBERS HAVING A DENIER OF FROM ABOUT 1 TO 5.5 AND CRIMPS COMPRISING HELICAL BENDS NUMBERING PER INCH 19 TO 35 TIMES THE SQUARE ROOT OF THE RECIPROCAL OF SAID DENIER, SAID STAPLE FBERS HAVING THE PROPERTY OF RETAINING SAID CRIMPS WHEN WET AND IN A RELAXED STATE, A QUANTITY OF ABOUT 1.5 GRAMS OF SAID STAPLE FIBERS HAVING AN INTERFIBER VOLUME IN THE DRY DTATE OF AT LEAST 1.750 CUBIC INCHES WHEN SUBJECTED TO A PRESSURE OF 0.5 POUND PER SQUARE INCH AND AN INTERFIBER VOLUME IN THE WET STATE OF AT LEAST 1.000 CUBIC INCHES WHEN SUBJECTED TO A PRESSURE OF 0.5 POUND PER SQUARE INCH, AND HAVING THE CPACITY TO ABSORB 26 TO 35 TIMES ITS WEIGHT OF WATER. 